21045 has 16 divisors (see below), whose sum is σ = 35712. Its totient is φ = 10560.

The previous prime is 21031. The next prime is 21059. The reversal of 21045 is 54012.

It is an interprime number because it is at equal distance from previous prime (21031) and next prime (21059).

It is not a de Polignac number, because 21045 - 2⁵ = 21013 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21045.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 315 + ... + 375.

It is an arithmetic number, because the mean of its divisors is an integer number (2232).

2²¹⁰⁴⁵ is an apocalyptic number.

It is an amenable number.

21045 is a deficient number, since it is larger than the sum of its proper divisors (14667).

21045 is a wasteful number, since it uses less digits than its factorization.

21045 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 92.

The product of its (nonzero) digits is 40, while the sum is 12.

The square root of 21045 is about 145.0689491242. The cubic root of 21045 is about 27.6089343057.

Adding to 21045 its reverse (54012), we get a palindrome (75057).

The spelling of 21045 in words is "twenty-one thousand, forty-five".